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Neurons are highly specialized for the processing and transmission of cellular signals. Given their diversity of functions performed in different parts of the nervous system, there is a wide variety in their shape, size, and electrochemical properties. For instance, the soma of a neuron can vary from 4 to 100 [[Micrometre|micrometers]] in diameter.<ref>{{cite web |first = Melissa |last = Davies |title = The Neuron: size comparison |url = https://www.ualberta.ca/~neuro/OnlineIntro/NeuronExample.htm |work = Neuroscience: A journey through the brain |date = 2002-04-09 |access-date = 2009-06-20}}</ref>

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神经元对细胞信号的处理和传送是高度专业化。鉴于它们在神经系统的不同部分所执行的功能的多样性，它们的形状、大小和电化学特性也有很大差异。例如，一个神经元的胞体的直径可以从4到100微米不等。 <ref>{{cite web |first = Melissa |last = Davies |title = The Neuron: size comparison |url = https://www.ualberta.ca/~neuro/OnlineIntro/NeuronExample.htm |work = Neuroscience: A journey through the brain |date = 2002-04-09 |access-date = 2009-06-20}}</ref>

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神经元对细胞信号的处理和传送是高度专业化。鉴于它们在神经系统的不同部分所执行的功能的多样性，它们的形状、大小和电化学特性也有很大差异。例如，一个神经元的胞体的直径可以从4到100微米不等。<ref>{{cite web |first = Melissa |last = Davies |title = The Neuron: size comparison |url = https://www.ualberta.ca/~neuro/OnlineIntro/NeuronExample.htm |work = Neuroscience: A journey through the brain |date = 2002-04-09 |access-date = 2009-06-20}}</ref>

*The '''[[Soma (biology)|soma]]''' is the body of the neuron. As it contains the [[cell nucleus|nucleus]], most [[protein biosynthesis|protein synthesis]] occurs here. The nucleus can range from 3 to 18 micrometers in diameter.<ref>{{cite web |first = Eric H. |last = Chudler | name-list-style = vanc |title = Brain Facts and Figures |url = http://faculty.washington.edu/chudler/facts.html |work = Neuroscience for Kids |access-date = 2009-06-20 }}</ref>

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*细胞体是神经元的主体。由于它含有细胞核，大多数蛋白质合成发生在这里。细胞核的直径可以从3到18微米不等。

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*细胞体是神经元的主体。由于它含有细胞核，大多数蛋白质合成发生在这里。细胞核的直径可以从3到18微米不等。<ref>{{cite web |first = Eric H. |last = Chudler | name-list-style = vanc |title = Brain Facts and Figures |url = http://faculty.washington.edu/chudler/facts.html |work = Neuroscience for Kids |access-date = 2009-06-20 }}</ref>

*The '''[[dendrites]]''' of a neuron are cellular extensions with many branches. This overall shape and structure is referred to metaphorically as a dendritic tree. This is where the majority of input to the neuron occurs via the [[dendritic spine]].

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The accepted view of the neuron attributes dedicated functions to its various anatomical components; however, dendrites and axons often act in ways contrary to their so-called main function.<ref>{{Cite web |date=2021-01-14 |title=16.7: Nervous System |url=https://bio.libretexts.org/Courses/Lumen_Learning/Book%3A_Fundamentals_of_Biology_I_(Lumen)/16%3A_Module_13%3A_Overview_of_Body_Systems/16.7%3A_Nervous_System |access-date=2022-02-28 |website=Biology LibreTexts |language=en}}</ref>

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公认的神经元观点将专门的功能归于其各种解剖成分；然而，树突和轴突的作用方式往往与它们所谓的主要功能相反。

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公认的神经元观点将专门的功能归于其各种解剖成分；然而，树突和轴突的作用方式往往与它们所谓的主要功能相反。<ref>{{Cite web |date=2021-01-14 |title=16.7: Nervous System |url=https://bio.libretexts.org/Courses/Lumen_Learning/Book%3A_Fundamentals_of_Biology_I_(Lumen)/16%3A_Module_13%3A_Overview_of_Body_Systems/16.7%3A_Nervous_System |access-date=2022-02-28 |website=Biology LibreTexts |language=en}}</ref>

[[File:Complete neuron cell diagram en.svg|thumb|right|Diagram of a typical myelinated vertebrate motor neuron典型的有髓的脊椎动物运动神经元示意图]]

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Fully differentiated neurons are permanently [[G0 phase|postmitotic]]<ref>{{cite journal | vauthors = Herrup K, Yang Y | title = Cell cycle regulation in the postmitotic neuron: oxymoron or new biology? | journal = Nature Reviews. Neuroscience | volume = 8 | issue = 5 | pages = 368–78 | date = May 2007 | pmid = 17453017 | doi = 10.1038/nrn2124 | s2cid = 12908713 }}</ref> however, stem cells present in the adult brain may regenerate functional neurons throughout the life of an organism (see [[neurogenesis]]). [[Astrocyte]]s are star-shaped [[glial cell]]s. They have been observed to turn into neurons by virtue of their stem cell-like characteristic of [[pluripotency]].

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完全分化的神经元是永久性的有丝分裂后的细胞，然而，存在于成人大脑中的干细胞可以在有机体的整个生命过程中再生出功能性神经元（见神经元的生成）。星形胶质细胞是星形的胶质细胞。它们已经被观察到可以凭借其类干细胞的多能性特征而变成神经元。

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完全分化的神经元是永久性的有丝分裂后的细胞，<ref>{{cite journal | vauthors = Herrup K, Yang Y | title = Cell cycle regulation in the postmitotic neuron: oxymoron or new biology? | journal = Nature Reviews. Neuroscience | volume = 8 | issue = 5 | pages = 368–78 | date = May 2007 | pmid = 17453017 | doi = 10.1038/nrn2124 | s2cid = 12908713 }}</ref>然而，存在于成人大脑中的干细胞可以在有机体的整个生命过程中再生出功能性神经元（见神经元的生成）。星形胶质细胞是星形的胶质细胞。它们已经被观察到可以凭借其类干细胞的多能性特征而变成神经元。

===Membrane膜结构===

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Numerous microscopic clumps called [[Nissl body|Nissl bodies]] (or Nissl substance) are seen when nerve cell bodies are stained with a basophilic ("base-loving") dye. These structures consist of [[Endoplasmic reticulum#Rough endoplasmic reticulum|rough endoplasmic reticulum]] and associated [[ribosomal RNA]]. Named after German psychiatrist and neuropathologist [[Franz Nissl]] (1860–1919), they are involved in protein synthesis and their prominence can be explained by the fact that nerve cells are very metabolically active. Basophilic dyes such as [[aniline]] or (weakly) [[haematoxylin]]<ref>{{cite book|title=State Hospitals Bulletin|url={{google books |plainurl=y |id=Wp8CAAAAYAAJ|page=378}}|year=1897|publisher=State Commission in Lunacy.|page=378}}</ref> highlight negatively charged components, and so bind to the phosphate backbone of the ribosomal RNA.

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当用嗜碱性（"嗜碱"）染料对神经细胞体进行染色时，可以看到许多称为尼氏体（或尼氏物质）的微观团块。这些结构由粗糙的内质网和相关的核糖体RNA组成。它们以德国精神病学家和神经病理学家弗朗茨-尼斯尔（1860-1919）的名字命名，参与蛋白质的合成，其突出性可以用神经细胞代谢非常活跃的事实来解释。嗜碱性染料如苯胺或（弱）血红蛋白会突出带负电的成分，因此与核糖体RNA的磷酸盐骨架结合。

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当用嗜碱性（"嗜碱"）染料对神经细胞体进行染色时，可以看到许多称为尼氏体（或尼氏物质）的微观团块。这些结构由粗糙的内质网和相关的核糖体RNA组成。它们以德国精神病学家和神经病理学家弗朗茨-尼斯尔（1860-1919）的名字命名，参与蛋白质的合成，其突出性可以用神经细胞代谢非常活跃的事实来解释。嗜碱性染料如苯胺或（弱）血红蛋白<ref>{{cite book|title=State Hospitals Bulletin|url={{google books |plainurl=y |id=Wp8CAAAAYAAJ|page=378}}|year=1897|publisher=State Commission in Lunacy.|page=378}}</ref>会突出带负电的成分，因此与核糖体RNA的磷酸盐骨架结合。

The cell body of a neuron is supported by a complex mesh of structural proteins called [[neurofilament]]s, which together with neurotubules (neuronal microtubules) are assembled into larger neurofibrils.<ref name="Webster">{{cite web |title=Medical Definition of Neurotubules |url=https://www.merriam-webster.com/medical/neurotubules |website=www.merriam-webster.com}}</ref> Some neurons also contain pigment granules, such as [[neuromelanin]] (a brownish-black pigment that is byproduct of synthesis of [[catecholamine]]s), and [[lipofuscin]] (a yellowish-brown pigment), both of which accumulate with age.<ref>{{cite journal | vauthors = Zecca L, Gallorini M, Schünemann V, Trautwein AX, Gerlach M, Riederer P, Vezzoni P, Tampellini D | title = Iron, neuromelanin and ferritin content in the substantia nigra of normal subjects at different ages: consequences for iron storage and neurodegenerative processes | journal = Journal of Neurochemistry | volume = 76 | issue = 6 | pages = 1766–73 | date = March 2001 | pmid = 11259494 | doi = 10.1046/j.1471-4159.2001.00186.x | s2cid = 31301135 }}</ref><ref>{{cite journal | vauthors = Herrero MT, Hirsch EC, Kastner A, Luquin MR, Javoy-Agid F, Gonzalo LM, Obeso JA, Agid Y | title = Neuromelanin accumulation with age in catecholaminergic neurons from Macaca fascicularis brainstem | journal = Developmental Neuroscience | volume = 15 | issue = 1 | pages = 37–48 | date = 1993 | pmid = 7505739 | doi = 10.1159/000111315 }}</ref><ref>{{cite journal | vauthors = Brunk UT, Terman A | title = Lipofuscin: mechanisms of age-related accumulation and influence on cell function | journal = Free Radical Biology & Medicine | volume = 33 | issue = 5 | pages = 611–9 | date = September 2002 | pmid = 12208347 | doi = 10.1016/s0891-5849(02)00959-0 }}</ref> Other structural proteins that are important for neuronal function are [[actin]] and the [[tubulin]] of [[microtubule]]s. [[Class III β-tubulin]] is found almost exclusively in neurons. Actin is predominately found at the tips of axons and dendrites during neuronal development. There the actin dynamics can be modulated via an interplay with microtubule.<ref>{{cite journal | vauthors = Zhao B, Meka DP, Scharrenberg R, König T, Schwanke B, Kobler O, Windhorst S, Kreutz MR, Mikhaylova M, Calderon de Anda F | title = Microtubules Modulate F-actin Dynamics during Neuronal Polarization | journal = Scientific Reports | volume = 7 | issue = 1 | pages = 9583 | date = August 2017 | pmid = 28851982 | pmc = 5575062 | doi = 10.1038/s41598-017-09832-8 | bibcode = 2017NatSR...7.9583Z }}</ref>

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神经元的细胞体由称为神经丝的结构蛋白的复杂网状结构支撑，它与神经管（神经元微管）一起被组装成较大的神经纤维。一些神经元还含有色素颗粒，如神经黑色素（一种棕黑色的色素，是儿茶酚胺合成的副产品）和脂褐素（一种黄褐色的色素），这两种物质都会随着年龄的增长而积累。对神经元功能很重要的其他结构蛋白是肌动蛋白和微管的管蛋白。第三类β-管蛋白几乎只在神经元中发现。在神经元发育过程中，肌动蛋白主要存在于轴突和树突的顶端。在那里，肌动蛋白的动态可以通过与微管的相互作用而被调节。

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神经元的细胞体由称为神经丝的结构蛋白的复杂网状结构支撑，它与神经管（神经元微管）一起被组装成较大的神经纤维。<ref name="Webster">{{cite web |title=Medical Definition of Neurotubules |url=https://www.merriam-webster.com/medical/neurotubules |website=www.merriam-webster.com}}</ref> 一些神经元还含有色素颗粒，如神经黑色素（一种棕黑色的色素，是儿茶酚胺合成的副产品）和脂褐素（一种黄褐色的色素），这两种物质都会随着年龄的增长而积累。<ref>{{cite journal | vauthors = Zecca L, Gallorini M, Schünemann V, Trautwein AX, Gerlach M, Riederer P, Vezzoni P, Tampellini D | title = Iron, neuromelanin and ferritin content in the substantia nigra of normal subjects at different ages: consequences for iron storage and neurodegenerative processes | journal = Journal of Neurochemistry | volume = 76 | issue = 6 | pages = 1766–73 | date = March 2001 | pmid = 11259494 | doi = 10.1046/j.1471-4159.2001.00186.x | s2cid = 31301135 }}</ref><ref>{{cite journal | vauthors = Herrero MT, Hirsch EC, Kastner A, Luquin MR, Javoy-Agid F, Gonzalo LM, Obeso JA, Agid Y | title = Neuromelanin accumulation with age in catecholaminergic neurons from Macaca fascicularis brainstem | journal = Developmental Neuroscience | volume = 15 | issue = 1 | pages = 37–48 | date = 1993 | pmid = 7505739 | doi = 10.1159/000111315 }}</ref><ref>{{cite journal | vauthors = Brunk UT, Terman A | title = Lipofuscin: mechanisms of age-related accumulation and influence on cell function | journal = Free Radical Biology & Medicine | volume = 33 | issue = 5 | pages = 611–9 | date = September 2002 | pmid = 12208347 | doi = 10.1016/s0891-5849(02)00959-0 }}</ref> 对神经元功能很重要的其他结构蛋白是肌动蛋白和微管的管蛋白。第三类β-管蛋白几乎只在神经元中发现。在神经元发育过程中，肌动蛋白主要存在于轴突和树突的顶端。在那里，肌动蛋白的动态可以通过与微管的相互作用而被调节。<ref>{{cite journal | vauthors = Zhao B, Meka DP, Scharrenberg R, König T, Schwanke B, Kobler O, Windhorst S, Kreutz MR, Mikhaylova M, Calderon de Anda F | title = Microtubules Modulate F-actin Dynamics during Neuronal Polarization | journal = Scientific Reports | volume = 7 | issue = 1 | pages = 9583 | date = August 2017 | pmid = 28851982 | pmc = 5575062 | doi = 10.1038/s41598-017-09832-8 | bibcode = 2017NatSR...7.9583Z }}</ref>

There are different internal structural characteristics between axons and dendrites. Typical axons almost never contain [[ribosomes]], except some in the initial segment. Dendrites contain granular endoplasmic reticulum or ribosomes, in diminishing amounts as the distance from the cell body increases.

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Neurons vary in shape and size and can be classified by their [[Morphology (biology)|morphology]] and function.<ref name="Al">{{cite book|last=Al|first=Martini, Frederic Et|title=Anatomy and Physiology' 2007 Ed.2007 Edition|url={{google books |plainurl=y |id=joJb82gVsLoC|page=288}}|publisher=Rex Bookstore, Inc.|isbn=978-971-23-4807-5|pages=288}}</ref> The anatomist [[Camillo Golgi]] grouped neurons into two types; type I with long axons used to move signals over long distances and type II with short axons, which can often be confused with dendrites. Type I cells can be further classified by the location of the soma. The basic morphology of type I neurons, represented by spinal [[motor neurons]], consists of a cell body called the soma and a long thin axon covered by a [[myelin sheath]]. The dendritic tree wraps around the cell body and receives signals from other neurons. The end of the axon has branching [[axon terminal]]s that release neurotransmitters into a gap called the [[synaptic cleft]] between the terminals and the dendrites of the next neuron.

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神经元的形状和大小各不相同，可按其形态和功能进行分类。解剖学家卡米洛-高尔基将神经元分为两类；I型有长轴，用于长距离移动信号；II型有短轴，常与树突相混淆。I型细胞可按胞体的位置进一步分类。以脊髓运动神经元为代表的I型神经元的基本形态包括一个称为胞体的细胞体和一个由髓鞘覆盖的细长轴突。树突树环绕着细胞体，接收来自其他神经元的信号。轴突的末端有分支的轴突终端，将神经递质释放到终端和下一个神经元树突之间的间隙中，称为突触间隙。

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神经元的形状和大小各不相同，可按其形态和功能进行分类。<ref name="Al">{{cite book|last=Al|first=Martini, Frederic Et|title=Anatomy and Physiology' 2007 Ed.2007 Edition|url={{google books |plainurl=y |id=joJb82gVsLoC|page=288}}|publisher=Rex Bookstore, Inc.|isbn=978-971-23-4807-5|pages=288}}</ref> 解剖学家卡米洛-高尔基将神经元分为两类：I型有长轴，用于长距离移动信号；II型有短轴，常与树突相混淆。I型细胞可按胞体的位置进一步分类。以脊髓运动神经元为代表的I型神经元的基本形态包括一个称为胞体的细胞体和一个由髓鞘覆盖的细长轴突。树突树环绕着细胞体，接收来自其他神经元的信号。轴突的末端有分支的轴突终端，将神经递质释放到终端和下一个神经元树突之间的间隙中，称为突触间隙。

===Structural classification结构分类===

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The distinction between excitatory and inhibitory neurotransmitters is not absolute. Rather, it depends on the class of chemical receptors present on the postsynaptic neuron. In principle, a single neuron, releasing a single neurotransmitter, can have excitatory effects on some targets, inhibitory effects on others, and modulatory effects on others still. For example, [[photoreceptor cell]]s in the retina constantly release the neurotransmitter glutamate in the absence of light. So-called OFF [[retinal bipolar cells|bipolar cells]] are, like most neurons, excited by the released glutamate. However, neighboring target neurons called ON bipolar cells are instead inhibited by glutamate, because they lack typical [[ionotropic receptor|ionotropic]] [[glutamate receptors]] and instead express a class of inhibitory [[metabotropic receptor|metabotropic]] glutamate receptors.<ref>{{cite journal | vauthors = Gerber U | title = Metabotropic glutamate receptors in vertebrate retina | journal = Documenta Ophthalmologica. Advances in Ophthalmology | volume = 106 | issue = 1 | pages = 83–7 | date = January 2003 | pmid = 12675489 | doi = 10.1023/A:1022477203420 | s2cid = 22296630 }}</ref> When light is present, the photoreceptors cease releasing glutamate, which relieves the ON bipolar cells from inhibition, activating them; this simultaneously removes the excitation from the OFF bipolar cells, silencing them.

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兴奋性和抑制性神经递质之间的区别不是绝对的。相反，它取决于突触后神经元上存在的化学受体的类别。原则上，一个神经元，释放一种神经递质，可以对某些目标产生兴奋作用，对其他目标产生抑制作用，对其他目标仍有调节作用。例如，视网膜上的感光细胞在没有光的情况下不断释放神经递质谷氨酸。像大多数神经元一样，所谓的关闭双极细胞被释放的谷氨酸所激发。然而，被称为ON双极细胞的邻近目标神经元反而受到谷氨酸的抑制，因为它们缺乏典型的离子型谷氨酸受体，而是表达一类抑制性的代谢型谷氨酸受体。当有光时，光感受器停止释放谷氨酸，这解除了ON双极细胞的抑制，激活了它们；这同时消除了OFF双极细胞的兴奋，使它们沉默。

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兴奋性和抑制性神经递质之间的区别不是绝对的。相反，它取决于突触后神经元上存在的化学受体的类别。原则上，一个神经元，释放一种神经递质，可以对某些目标产生兴奋作用，对其他目标产生抑制作用，对其他目标仍有调节作用。例如，视网膜上的感光细胞在没有光的情况下不断释放神经递质谷氨酸。像大多数神经元一样，所谓的关闭双极细胞被释放的谷氨酸所激发。然而，被称为ON双极细胞的邻近目标神经元反而受到谷氨酸的抑制，因为它们缺乏典型的离子型谷氨酸受体，而是表达一类抑制性的代谢型谷氨酸受体。<ref>{{cite journal | vauthors = Gerber U | title = Metabotropic glutamate receptors in vertebrate retina | journal = Documenta Ophthalmologica. Advances in Ophthalmology | volume = 106 | issue = 1 | pages = 83–7 | date = January 2003 | pmid = 12675489 | doi = 10.1023/A:1022477203420 | s2cid = 22296630 }}</ref>当有光时，光感受器停止释放谷氨酸，这解除了ON双极细胞的抑制，激活了它们；这同时消除了OFF双极细胞的兴奋，使它们沉默。

It is possible to identify the type of inhibitory effect a presynaptic neuron will have on a postsynaptic neuron, based on the proteins the presynaptic neuron expresses. [[Parvalbumin]]-expressing neurons typically dampen the output signal of the postsynaptic neuron in the [[visual cortex]], whereas [[somatostatin]]-expressing neurons typically block dendritic inputs to the postsynaptic neuron.<ref name="pmid22878717">{{cite journal | vauthors = Wilson NR, Runyan CA, Wang FL, Sur M | title = Division and subtraction by distinct cortical inhibitory networks in vivo | journal = Nature | volume = 488 | issue = 7411 | pages = 343–8 | date = August 2012 | pmid = 22878717 | pmc = 3653570 | doi = 10.1038/nature11347 | bibcode = 2012Natur.488..343W | hdl = 1721.1/92709 }}</ref>

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根据突触前神经元表达的蛋白质，可以确定突触前神经元对突触后神经元的抑制作用的类型。表达副白蛋白的神经元通常会抑制视觉皮层中突触后神经元的输出信号，而表达躯干素的神经元通常会阻断突触后神经元的树突输入。

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根据突触前神经元表达的蛋白质，可以确定突触前神经元对突触后神经元的抑制作用的类型。表达副白蛋白的神经元通常会抑制视觉皮层中突触后神经元的输出信号，而表达躯干素的神经元通常会阻断突触后神经元的树突输入。<ref name="pmid22878717">{{cite journal | vauthors = Wilson NR, Runyan CA, Wang FL, Sur M | title = Division and subtraction by distinct cortical inhibitory networks in vivo | journal = Nature | volume = 488 | issue = 7411 | pages = 343–8 | date = August 2012 | pmid = 22878717 | pmc = 3653570 | doi = 10.1038/nature11347 | bibcode = 2012Natur.488..343W | hdl = 1721.1/92709 }}</ref>

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====Discharge patterns放电模式====

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Neurons have intrinsic electroresponsive properties like intrinsic transmembrane voltage [[Neural oscillation|oscillatory]] patterns.<ref name="llinas2014">{{cite journal | vauthors = Llinás RR | title = Intrinsic electrical properties of mammalian neurons and CNS function: a historical perspective | journal = Frontiers in Cellular Neuroscience | volume = 8 | pages = 320 | date = 2014-01-01 | pmid = 25408634 | pmc = 4219458 | doi = 10.3389/fncel.2014.00320 | doi-access = free }}</ref> So neurons can be classified according to their [[electrophysiology|electrophysiological]] characteristics:

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~~神经元具有内在的电反应特性，如内在的跨膜电压振荡模式。因此，可以根据神经元的电生理特性对其进行分类：~~

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神经元具有内在的电反应特性，如内在的跨膜电压振荡模式。<ref name="llinas2014">{{cite journal | vauthors = Llinás RR | title = Intrinsic electrical properties of mammalian neurons and CNS function: a historical perspective | journal = Frontiers in Cellular Neuroscience | volume = 8 | pages = 320 | date = 2014-01-01 | pmid = 25408634 | pmc = 4219458 | doi = 10.3389/fncel.2014.00320 | doi-access = free }}</ref>因此，可以根据神经元的电生理特性对其进行分类：

*Tonic or regular spiking. Some neurons are typically constantly (tonically) active, typically firing at a constant frequency. Example: interneurons in neurostriatum.

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*紧张性或规律性棘波。一些神经元通常持续（紧张地）活跃，通常以恒定的频率放电。例如：神经干细胞中的interneurons。

*瞬变性或爆发性。爆发性放电的神经元被称为瞬变性的。

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*快闪性。一些神经元因其高放电率而引人注目，例如某些类型的皮质抑制性中间神经元、苍白球、视网膜神经节细胞。

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*快闪性。一些神经元因其高放电率而引人注目，例如某些类型的皮质抑制性中间神经元、苍白球、视网膜神经节细胞。<ref>{{cite conference | title = Ion conductances related to shaping the repetitive firing in rat retinal ganglion cells | vauthors = Kolodin YO, Veselovskaia NN, Veselovsky NS, Fedulova SA | conference = Acta Physiologica Congress | url = http://www.blackwellpublishing.com/aphmeeting/abstract.asp?MeetingID=&id=61198 | access-date = 2009-06-20 | archive-url = https://web.archive.org/web/20121007164451/http://www.blackwellpublishing.com/aphmeeting/abstract.asp?MeetingID=&id=61198 | archive-date = 2012-10-07 | url-status = dead }}</ref><ref>{{cite web|url=http://ykolodin.50webs.com/ |title=Ionic conductances underlying excitability in tonically firing retinal ganglion cells of adult rat |publisher=Ykolodin.50webs.com |date=2008-04-27 |access-date=2013-02-16}}</ref>

====Neurotransmitter神经递质 ====

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*羟色胺能神经元——羟色胺。羟色胺（5-Hydroxytryptamine，5-HT）可以起到兴奋性或抑制性作用。在其四个5-HT受体类别中，3个是GPCR，1个是配体门控的阳离子通道。羟色胺由色氨酸经色氨酸羟化酶合成，然后再经脱羧酶进一步合成。突触后神经元缺乏5-HT与抑郁症有关。阻断突触前5-羟色胺转运体的药物被用于治疗，如百忧解和左洛复。

*嘌呤神经元——ATP。ATP是一种同时作用于配体门控离子通道（P2X受体）和GPCRs（P2Y）受体的神经递质。然而，ATP最有名的是作为一种共传导剂。这种嘌呤信号也可以由其他嘌呤介导，如腺苷，它特别作用于P2Y受体。

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*组胺能神经元——组胺。组胺是一种单胺类神经递质和神经调节剂。产生组胺的神经元存在于下丘脑的管状乳头核。组胺参与唤醒和调节睡眠/觉醒行为。

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*组胺能神经元——组胺。组胺是一种单胺类神经递质和神经调节剂。产生组胺的神经元存在于下丘脑的管状乳头核。<ref>{{cite journal | vauthors = Scammell TE, Jackson AC, Franks NP, Wisden W, Dauvilliers Y | title = Histamine: neural circuits and new medications | journal = Sleep | volume = 42 | issue = 1 | date = January 2019 | pmid = 30239935 | pmc = 6335869 | doi = 10.1093/sleep/zsy183 }}</ref> 组胺参与唤醒和调节睡眠/觉醒行为。

====Multimodel classification多模式分类====

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Since 2012 there has been a push from the cellular and computational neuroscience community to come up with a universal classification of neurons that will apply to all neurons in the brain as well as across species. This is done by considering the three essential qualities of all neurons: electrophysiology, morphology, and the individual transcriptome of the cells. Besides being universal this classification has the advantage of being able to classify astrocytes as well. A method called Patch-Seq in which all three qualities can be measured at once is used extensively by the Allen Institute for Brain Science.<ref>{{cite web |url=https://www.news-medical.net/news/20201203/Patch-seq-technique-helps-depict-the-variation-of-neural-cells-in-the-brain.aspx |title=Patch-seq technique helps depict the variation of neural cells in the brain |work=News-medical.net |date=3 December 2020 |access-date=26 August 2021 |url-status=live}}</ref>

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自2012年以来，细胞和计算神经科学界一直在推动提出一个通用的神经元分类，该分类将适用于大脑中的所有神经元以及跨物种。这是通过考虑所有神经元的三个基本属性来实现的：电生理学、形态学和细胞的个体转录组。除了具有普遍性之外，这种分类法还有一个优点，就是能够对星形胶质细胞进行分类。艾伦脑科学研究所广泛使用一种叫做Patch-Seq的方法，可以同时测量所有三种属性。

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自2012年以来，细胞和计算神经科学界一直在推动提出一个通用的神经元分类，该分类将适用于大脑中的所有神经元以及跨物种。这是通过考虑所有神经元的三个基本属性来实现的：电生理学、形态学和细胞的个体转录组。除了具有普遍性之外，这种分类法还有一个优点，就是能够对星形胶质细胞进行分类。艾伦脑科学研究所广泛使用一种叫做Patch-Seq的方法，可以同时测量所有三种属性。<ref>{{cite web |url=https://www.news-medical.net/news/20201203/Patch-seq-technique-helps-depict-the-variation-of-neural-cells-in-the-brain.aspx |title=Patch-seq technique helps depict the variation of neural cells in the brain |work=News-medical.net |date=3 December 2020 |access-date=26 August 2021 |url-status=live}}</ref>

==Connectivity连接性==

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Synapses can be [[EPSP|excitatory]] or [[IPSP|inhibitory]], either increasing or decreasing activity in the target neuron, respectively. Some neurons also communicate via electrical synapses, which are direct, electrically conductive [[gap junction|junctions]] between cells.<ref>{{cite book |last1=Macpherson |first1=Gordon |title=Black's Medical Dictionary |date=2002 |publisher=Scarecrow Press |location=Lanham, MD |isbn=0810849844 |pages=431–434 |edition=40 }}</ref>

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突触可以是兴奋性的或抑制性的，分别增加或减少目标神经元的活动。一些神经元还通过电突触进行交流，电突触是细胞之间直接的、导电的连接点。

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突触可以是兴奋性的或抑制性的，分别增加或减少目标神经元的活动。一些神经元还通过电突触进行交流，电突触是细胞之间直接的、导电的连接点。<ref>{{cite book |last1=Macpherson |first1=Gordon |title=Black's Medical Dictionary |date=2002 |publisher=Scarecrow Press |location=Lanham, MD |isbn=0810849844 |pages=431–434 |edition=40 }}</ref>

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When an action potential reaches the axon terminal, it opens [[Voltage-dependent calcium channel|voltage-gated calcium channels]], allowing [[Calcium in biology|calcium ions]] to enter the terminal. Calcium causes [[synaptic vesicles]] filled with neurotransmitter molecules to fuse with the membrane, releasing their contents into the synaptic cleft. The neurotransmitters diffuse across the synaptic cleft and activate receptors on the postsynaptic neuron. High cytosolic calcium in the [[axon terminal]] triggers mitochondrial calcium uptake, which, in turn, activates mitochondrial [[energy metabolism]] to produce [[Adenosine triphosphate|ATP]] to support continuous neurotransmission.<ref name="pmid23746507">{{cite journal | vauthors = Ivannikov MV, Macleod GT | title = Mitochondrial free Ca²⁺ levels and their effects on energy metabolism in Drosophila motor nerve terminals | journal = Biophysical Journal | volume = 104 | issue = 11 | pages = 2353–61 | date = June 2013 | pmid = 23746507 | pmc = 3672877 | doi = 10.1016/j.bpj.2013.03.064 | bibcode = 2013BpJ...104.2353I }}</ref>

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当动作电位到达轴突末端时，它打开电压门控的钙离子通道，允许钙离子进入末端。钙离子使充满神经递质分子的突触小泡与膜融合，将其内容释放到突触间隙中。神经递质在突触间隙中扩散，激活突触后神经元上的受体。轴突末端的高细胞钙引发线粒体钙吸收，这反过来又激活了线粒体的能量代谢，产生ATP以支持持续的神经传递。

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当动作电位到达轴突末端时，它打开电压门控的钙离子通道，允许钙离子进入末端。钙离子使充满神经递质分子的突触小泡与膜融合，将其内容释放到突触间隙中。神经递质在突触间隙中扩散，激活突触后神经元上的受体。轴突末端的高细胞钙引发线粒体钙吸收，这反过来又激活了线粒体的能量代谢，产生ATP以支持持续的神经传递。<ref name="pmid23746507">{{cite journal | vauthors = Ivannikov MV, Macleod GT | title = Mitochondrial free Ca²⁺ levels and their effects on energy metabolism in Drosophila motor nerve terminals | journal = Biophysical Journal | volume = 104 | issue = 11 | pages = 2353–61 | date = June 2013 | pmid = 23746507 | pmc = 3672877 | doi = 10.1016/j.bpj.2013.03.064 | bibcode = 2013BpJ...104.2353I }}</ref>

An [[autapse]] is a synapse in which a neuron's axon connects to its own dendrites.

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[[File:Axon Propagation.svg|thumb|563x563px|An annotated diagram of the stages of an action potential propagating down an axon including the role of ion concentration and pump and channel proteins.一个动作电位沿轴突传播的阶段的注释图，包括离子浓度和泵及通道蛋白的作用。]]

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人脑有大约8.6 x 1010（86亿）个神经元。每个神经元平均有7000个与其他神经元的突触连接。据估计，一个三岁孩子的大脑大约有1015个突触（1万亿）。这个数字随着年龄的增长而下降，到成年后趋于稳定。对成年人的估计有所不同，从1014到5 x 1014个突触（100到500万亿）不等。

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人脑有大约8.6 x 1010（86亿）个神经元。<ref>{{ cite journal | vauthors = Herculano-Houzel S | title = The human brain in numbers: a linearly scaled-up primate brain | journal = Frontiers in Human Neuroscience | volume = 3 | pages = 31 | date = November 2009 | pmid = 19915731 | doi = 10.3389/neuro.09.031.2009 | pmc = 2776484 | doi-access = free }}</ref>每个神经元平均有7000个与其他神经元的突触连接。据估计，一个三岁孩子的大脑大约有1015个突触（1万亿）。这个数字随着年龄的增长而下降，到成年后趋于稳定。对成年人的估计有所不同，从1014到5 x 1014个突触（100到500万亿）不等。<ref>{{cite journal | vauthors = Drachman DA | title = Do we have brain to spare? | journal = Neurology | volume = 64 | issue = 12 | pages = 2004–5 | date = June 2005 | pmid = 15985565 | doi = 10.1212/01.WNL.0000166914.38327.BB | s2cid = 38482114 }}</ref>

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=== Nonelectrochemical signaling非电化学信号传递 ===

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除了电和化学信号，研究表明健康人脑中的神经元还可以通过以下方式交流：

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*~~树突棘扩大产生的力~~

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*树突棘扩大产生的力。<ref>{{cite journal |last1=Ucar |first1=Hasan |last2=Watanabe |first2=Satoshi |last3=Noguchi |first3=Jun |last4=Morimoto |first4=Yuichi |last5=Iino |first5=Yusuke |last6=Yagishita |first6=Sho |last7=Takahashi |first7=Noriko |last8=Kasai |first8=Haruo |title=Mechanical actions of dendritic-spine enlargement on presynaptic exocytosis |journal=Nature |date=December 2021 |volume=600 |issue=7890 |pages=686–689 |doi=10.1038/s41586-021-04125-7 |language=en |issn=1476-4687}} Lay summary: {{cite news |title=Forceful synapses reveal mechanical interactions in the brain |url=https://www.nature.com/articles/d41586-021-03516-0 |access-date=21 February 2022 |work=Nature |date=24 November 2021 |language=en |doi=10.1038/d41586-021-03516-0}}</ref>

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*蛋白质的转移--经神经元转运蛋白（TNTPs）。

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*蛋白质的转移--经神经元转运蛋白（TNTPs）。<ref>{{cite news |title=Researchers discover new type of cellular communication in the brain |url=https://medicalxpress.com/news/2022-01-cellular-brain.html |access-date=12 February 2022 |work=The Scripps Research Institute |language=en}}</ref><ref>{{cite journal |last1=Schiapparelli |first1=Lucio M. |last2=Sharma |first2=Pranav |last3=He |first3=Hai-Yan |last4=Li |first4=Jianli |last5=Shah |first5=Sahil H. |last6=McClatchy |first6=Daniel B. |last7=Ma |first7=Yuanhui |last8=Liu |first8=Han-Hsuan |last9=Goldberg |first9=Jeffrey L. |last10=Yates |first10=John R. |last11=Cline |first11=Hollis T. |title=Proteomic screen reveals diverse protein transport between connected neurons in the visual system |journal=Cell Reports |date=25 January 2022 |volume=38 |issue=4 |doi=10.1016/j.celrep.2021.110287 |language=English |issn=2211-1247}}</ref>

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They can also get modulated by input from the environment and [[hormone]]s released from other parts of the organism,<ref>{{cite journal |last1=Levitan |first1=Irwin B. |last2=Kaczmarek |first2=Leonard K. |title=Electrical Signaling in Neurons |doi=10.1093/med/9780199773893.001.0001/med-9780199773893-chapter-3 |publisher=Oxford University Press}}</ref> which could be influenced more or less directly by neurons. This also applies to [[neurotrophin]]s such as [[BDNF]]. The [[gut microbiome]] is also connected with the brain.<ref>{{cite journal |last1=O’Leary |first1=Olivia F. |last2=Ogbonnaya |first2=Ebere S. |last3=Felice |first3=Daniela |last4=Levone |first4=Brunno R. |last5=C. Conroy |first5=Lorraine |last6=Fitzgerald |first6=Patrick |last7=Bravo |first7=Javier A. |last8=Forsythe |first8=Paul |last9=Bienenstock |first9=John |last10=Dinan |first10=Timothy G. |last11=Cryan |first11=John F. |title=The vagus nerve modulates BDNF expression and neurogenesis in the hippocampus |journal=European Neuropsychopharmacology |date=1 February 2018 |volume=28 |issue=2 |pages=307–316 |doi=10.1016/j.euroneuro.2017.12.004 |language=en |issn=0924-977X}}</ref>

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它们也可以被来自环境的输入和机体其他部分释放的激素所调控， ~~这些都可以或多或少地被神经元直接影响。这也适用于神经营养素，如BDNF。肠道微生物组也与大脑有关。~~

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它们也可以被来自环境的输入和机体其他部分释放的激素所调控，<ref>{{cite journal |last1=Levitan |first1=Irwin B. |last2=Kaczmarek |first2=Leonard K. |title=Electrical Signaling in Neurons |doi=10.1093/med/9780199773893.001.0001/med-9780199773893-chapter-3 |publisher=Oxford University Press}}</ref> 这些都可以或多或少地被神经元直接影响。这也适用于神经营养素，如BDNF。肠道微生物组也与大脑有关。<ref>{{cite journal |last1=O’Leary |first1=Olivia F. |last2=Ogbonnaya |first2=Ebere S. |last3=Felice |first3=Daniela |last4=Levone |first4=Brunno R. |last5=C. Conroy |first5=Lorraine |last6=Fitzgerald |first6=Patrick |last7=Bravo |first7=Javier A. |last8=Forsythe |first8=Paul |last9=Bienenstock |first9=John |last10=Dinan |first10=Timothy G. |last11=Cryan |first11=John F. |title=The vagus nerve modulates BDNF expression and neurogenesis in the hippocampus |journal=European Neuropsychopharmacology |date=1 February 2018 |volume=28 |issue=2 |pages=307–316 |doi=10.1016/j.euroneuro.2017.12.004 |language=en |issn=0924-977X}}</ref>

==Mechanisms for propagating action potentials动作电位的传播机制==

In 1937 [[John Zachary Young]] suggested that the [[squid giant axon]] could be used to study neuronal electrical properties.<ref>{{cite web |first = Eric H. |last = Chudler | name-list-style = vanc |title = Milestones in Neuroscience Research |url = http://faculty.washington.edu/chudler/hist.html |work = Neuroscience for Kids |access-date = 2009-06-20}}</ref> It is larger than but similar to human neurons, making it easier to study. By inserting electrodes into the squid giant axons, accurate measurements were made of the [[membrane potential]].

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1937年，约翰-扎卡里-杨提出，乌贼巨大轴突可用于研究神经元的电特性。它比人类神经元大，但与人类神经元相似，因此更容易研究。通过将电极插入乌贼巨轴突，对膜电位进行了精确测量。

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1937年，约翰-扎卡里-杨提出，乌贼巨大轴突可用于研究神经元的电特性。<ref>{{cite web |first = Eric H. |last = Chudler | name-list-style = vanc |title = Milestones in Neuroscience Research |url = http://faculty.washington.edu/chudler/hist.html |work = Neuroscience for Kids |access-date = 2009-06-20}}</ref>它比人类神经元大，但与人类神经元相似，因此更容易研究。通过将电极插入乌贼巨轴突，对膜电位进行了精确测量。

The cell membrane of the axon and soma contain voltage-gated ion channels that allow the neuron to generate and propagate an electrical signal (an action potential). Some neurons also generate [[subthreshold membrane potential oscillations]]. These signals are generated and propagated by charge-carrying [[ions]] including sodium (Na+), potassium (K+), chloride (Cl−), and [[Calcium signaling|calcium (Ca2+)]].

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Several stimuli can activate a neuron leading to electrical activity, including [[Mechanoreceptor|pressure]], stretch, chemical transmitters, and changes of the electric potential across the cell membrane.<ref>{{cite web|first1=Joe |last1=Patlak |first2=Ray |last2=Gibbons | name-list-style = vanc |title=Electrical Activity of Nerves |url=http://physioweb.med.uvm.edu/cardiacep/EP/nervecells.htm |work=Action Potentials in Nerve Cells |date=2000-11-01 |access-date=2009-06-20 |url-status=dead |archive-url=https://web.archive.org/web/20090827220335/http://physioweb.med.uvm.edu/cardiacep/EP/nervecells.htm |archive-date=August 27, 2009 }}</ref> Stimuli cause specific ion-channels within the cell membrane to open, leading to a flow of ions through the cell membrane, changing the membrane potential. Neurons must maintain the specific electrical properties that define their neuron type.<ref name="Harris-Warrick">{{cite journal |last1=Harris-Warrick |first1=RM |title=Neuromodulation and flexibility in Central Pattern Generator networks. |journal=Current Opinion in Neurobiology |date=October 2011 |volume=21 |issue=5 |pages=685–92 |doi=10.1016/j.conb.2011.05.011 |pmid=21646013|pmc=3171584 }}</ref>

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有几种刺激可以激活神经元，导致电活动，包括压力、拉伸、化学传导物和细胞膜上的电势变化。 ~~刺激导致细胞膜内特定的离子通道打开，使得离子流经细胞膜，改变膜电位。神经元必须保持界定其神经元类型的特定电特性。~~

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有几种刺激可以激活神经元，导致电活动，包括压力、拉伸、化学传导物和细胞膜上的电势变化。<ref>{{cite web|first1=Joe |last1=Patlak |first2=Ray |last2=Gibbons | name-list-style = vanc |title=Electrical Activity of Nerves |url=http://physioweb.med.uvm.edu/cardiacep/EP/nervecells.htm |work=Action Potentials in Nerve Cells |date=2000-11-01 |access-date=2009-06-20 |url-status=dead |archive-url=https://web.archive.org/web/20090827220335/http://physioweb.med.uvm.edu/cardiacep/EP/nervecells.htm |archive-date=August 27, 2009 }}</ref>刺激导致细胞膜内特定的离子通道打开，使得离子流经细胞膜，改变膜电位。神经元必须保持界定其神经元类型的特定电特性。<ref name="Harris-Warrick">{{cite journal |last1=Harris-Warrick |first1=RM |title=Neuromodulation and flexibility in Central Pattern Generator networks. |journal=Current Opinion in Neurobiology |date=October 2011 |volume=21 |issue=5 |pages=685–92 |doi=10.1016/j.conb.2011.05.011 |pmid=21646013|pmc=3171584 }}</ref>

Thin neurons and axons require less [[metabolism|metabolic]] expense to produce and carry action potentials, but thicker axons convey impulses more rapidly. To minimize metabolic expense while maintaining rapid conduction, many neurons have insulating sheaths of [[myelin]] around their axons. The sheaths are formed by [[glia]]l cells: [[oligodendrocyte]]s in the central nervous system and [[Schwann cell]]s in the peripheral nervous system. The sheath enables action potentials to travel [[saltatory conduction|faster]] than in unmyelinated axons of the same diameter, whilst using less energy. The myelin sheath in peripheral nerves normally runs along the axon in sections about 1 mm long, punctuated by unsheathed [[node of Ranvier|nodes of Ranvier]], which contain a high density of voltage-gated ion channels. [[Multiple sclerosis]] is a neurological disorder that results from demyelination of axons in the central nervous system.

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[[Neural coding]] is concerned with how sensory and other information is represented in the brain by neurons. The main goal of studying neural coding is to characterize the relationship between the [[Stimulus (physiology)|stimulus]] and the individual or [[Neural ensemble|ensemble]] neuronal responses, and the relationships among the electrical activities of the neurons within the ensemble.<ref name="Brown">{{cite journal | vauthors = Brown EN, Kass RE, Mitra PP | title = Multiple neural spike train data analysis: state-of-the-art and future challenges | journal = Nature Neuroscience | volume = 7 | issue = 5 | pages = 456–61 | date = May 2004 | pmid = 15114358 | doi = 10.1038/nn1228 | s2cid = 562815 }}</ref> It is thought that neurons can encode both [[Digital data|digital]] and [[analog signal|analog]] information.<ref>{{cite book | vauthors = Thorpe SJ |chapter=Spike arrival times: A highly efficient coding scheme for neural networks |chapter-url= http://pop.cerco.ups-tlse.fr/fr_vers/documents/thorpe_sj_90_91.pdf |pages= 91–94 |title=Parallel processing in neural systems and computers| veditors = Eckmiller R, Hartmann G, Hauske G |date=1990|publisher=North-Holland|isbn=9780444883902 |url={{google books |plainurl=y |id=boBqAAAAMAAJ}}|language=en|archive-url=https://web.archive.org/web/20120215151304/http://pop.cerco.ups-tlse.fr/fr_vers/documents/thorpe_sj_90_91.pdf|archive-date=2012-02-15}}</ref>

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神经编码关注的是感觉和其他信息如何在大脑中被神经元所表达。研究神经编码的主要目的是描述刺激与单个或集合神经元反应之间的关系，以及集合内神经元电活动之间的关系。人们认为，神经元既可以编码数字信息，也可以编码模拟信息。

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神经编码关注的是感觉和其他信息如何在大脑中被神经元所表达。研究神经编码的主要目的是描述刺激与单个或集合神经元反应之间的关系，以及集合内神经元电活动之间的关系。<ref name="Brown">{{cite journal | vauthors = Brown EN, Kass RE, Mitra PP | title = Multiple neural spike train data analysis: state-of-the-art and future challenges | journal = Nature Neuroscience | volume = 7 | issue = 5 | pages = 456–61 | date = May 2004 | pmid = 15114358 | doi = 10.1038/nn1228 | s2cid = 562815 }}</ref>人们认为，神经元既可以编码数字信息，也可以编码模拟信息。<ref>{{cite book | vauthors = Thorpe SJ |chapter=Spike arrival times: A highly efficient coding scheme for neural networks |chapter-url= http://pop.cerco.ups-tlse.fr/fr_vers/documents/thorpe_sj_90_91.pdf |pages= 91–94 |title=Parallel processing in neural systems and computers| veditors = Eckmiller R, Hartmann G, Hauske G |date=1990|publisher=North-Holland|isbn=9780444883902 |url={{google books |plainurl=y |id=boBqAAAAMAAJ}}|language=en|archive-url=https://web.archive.org/web/20120215151304/http://pop.cerco.ups-tlse.fr/fr_vers/documents/thorpe_sj_90_91.pdf|archive-date=2012-02-15}}</ref>

==All-or-none principle全有或全无原则==

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The conduction of nerve impulses is an example of an [[All-or-none law|all-or-none]] response. In other words, if a neuron responds at all, then it must respond completely. Greater intensity of stimulation, like brighter image/louder sound, does not produce a stronger signal, but can increase firing frequency.<ref name=":0" />{{Rp|31}} Receptors respond in different ways to stimuli. Slowly adapting or [[tonic (physiology)|tonic receptors]] respond to steady stimulus and produce a steady rate of firing. Tonic receptors most often respond to increased intensity of stimulus by increasing their firing frequency, usually as a power function of stimulus plotted against impulses per second. This can be likened to an intrinsic property of light where greater intensity of a specific frequency (color) requires more photons, as the photons can't become "stronger" for a specific frequency.

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神经冲动的传导是一个全有或全无反应的例子。换句话说，如果一个神经元有任何反应，那么它必须完全响应。更大的刺激强度，如更亮的图像/更响的声音，不会产生更强的信号，但可以增加放电频率。[34]：31受体以不同方式回应刺激。缓慢适应的或紧张性的受体对稳定的刺激作出响应，并产生稳定的放电率。紧张性受体最常通过增加其放电频率对刺激强度的增加作出反应，通常是一个与每秒钟的脉冲相关的刺激的幂函数。这可以比喻为光的内在属性，即一个特定频率（颜色）的更大强度需要更多的光子，因为光子不能对一个特定频率变得 "更强"。

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神经冲动的传导是一个全有或全无反应的例子。换句话说，如果一个神经元有任何反应，那么它必须完全响应。更大的刺激强度，如更亮的图像/更响的声音，不会产生更强的信号，但可以增加放电频率。<ref name=":0" />{{Rp|31}}受体以不同方式回应刺激。缓慢适应的或紧张性的受体对稳定的刺激作出响应，并产生稳定的放电率。紧张性受体最常通过增加其放电频率对刺激强度的增加作出反应，通常是一个与每秒钟的脉冲相关的刺激的幂函数。这可以比喻为光的内在属性，即一个特定频率（颜色）的更大强度需要更多的光子，因为光子不能对一个特定频率变得 "更强"。

Other receptor types include quickly adapting or phasic receptors, where firing decreases or stops with steady stimulus; examples include [[Human skin|skin]] which, when touched causes neurons to fire, but if the object maintains even pressure, the neurons stop firing. The neurons of the skin and muscles that are responsive to pressure and vibration have filtering accessory structures that aid their function.

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The [[pacinian corpuscle]] is one such structure. It has concentric layers like an onion, which form around the axon terminal. When pressure is applied and the corpuscle is deformed, mechanical stimulus is transferred to the axon, which fires. If the pressure is steady, stimulus ends; thus, typically these neurons respond with a transient depolarization during the initial deformation and again when the pressure is removed, which causes the corpuscle to change shape again. Other types of adaptation are important in extending the function of a number of other neurons.<ref>{{cite book | last1 = Eckert | first1 = Roger | last2 = Randall | first2 = David | name-list-style = vanc | title = Animal physiology: mechanisms and adaptations | year = 1983 | publisher = W.H. Freeman | location = San Francisco | isbn = 978-0-7167-1423-1 | page = [https://archive.org/details/animalphysiology0000ecke/page/239 239] | url = https://archive.org/details/animalphysiology0000ecke/page/239 }}</ref>

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帕西尼氏小体就是这样一个结构。它有像洋葱一样的同心层，围绕着轴突终端形成。当施加压力使小体变形时，机械刺激被转移到轴突上，轴突就会放电。如果压力是稳定的，刺激就会结束；因此，通常这些神经元在最初的变形过程中会有短暂的去极化反应，而当压力被移除时又会有短暂的去极化反应，从而使小体再次改变形状。其他类型的适应对扩展其他一些神经元的功能很重要。[35]

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帕西尼氏小体就是这样一个结构。它有像洋葱一样的同心层，围绕着轴突终端形成。当施加压力使小体变形时，机械刺激被转移到轴突上，轴突就会放电。如果压力是稳定的，刺激就会结束；因此，通常这些神经元在最初的变形过程中会有短暂的去极化反应，而当压力被移除时又会有短暂的去极化反应，从而使小体再次改变形状。其他类型的适应对扩展其他一些神经元的功能很重要。<ref>{{cite book | last1 = Eckert | first1 = Roger | last2 = Randall | first2 = David | name-list-style = vanc | title = Animal physiology: mechanisms and adaptations | year = 1983 | publisher = W.H. Freeman | location = San Francisco | isbn = 978-0-7167-1423-1 | page = [https://archive.org/details/animalphysiology0000ecke/page/239 239] | url = https://archive.org/details/animalphysiology0000ecke/page/239 }}</ref>

==Etymology and spelling词源和拼写==

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The German anatomist [[Heinrich Wilhelm Gottfried von Waldeyer-Hartz|Heinrich Wilhelm Waldeyer]] introduced the term ''neuron'' in 1891,<ref name="finger"/> based on the [[Greek language|ancient Greek]] νεῦρον ''neuron'' 'sinew, cord, nerve'.<ref name="oed">''[[Oxford English Dictionary]]'', 3rd edition, 2003, ''s.v.''</ref>

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德国解剖学家Heinrich Wilhelm Waldeyer于1891年提出了神经元一词，[36]其依据是古希腊语νεῦρον neuron's sinew, cord, nerve'。[37]

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德国解剖学家Heinrich Wilhelm Waldeyer于1891年提出了神经元一词，[36]其依据是古希腊语νεῦρον neuron's sinew, cord, nerve'。<ref name="finger"/> based on the [[Greek language|ancient Greek]] νεῦρον ''neuron'' 'sinew, cord, nerve'.<ref name="oed">''[[Oxford English Dictionary]]'', 3rd edition, 2003, ''s.v.''</ref>

The word was adopted in French with the spelling ''neurone''. That spelling was also used by many writers in English,<ref name="mehta">{{cite journal | vauthors = Mehta AR, Mehta PR, Anderson SP, MacKinnon BL, Compston A | title = Grey Matter Etymology and the neuron(e) | journal = Brain | volume = 143 | issue = 1 | pages = 374–379 | date = January 2020 | pmid = 31844876 | pmc = 6935745 | doi = 10.1093/brain/awz367 | url = }}</ref> but has now become rare in American usage and uncommon in British usage.<ref name="ngram">{{cite web |title=Google Books Ngram Viewer |url=https://books.google.com/ngrams/graph?content=neuron%2Cneurone&year_start=1900&year_end=2008&case_insensitive=on&corpus=15&smoothing=3&direct_url=t4%3B%2Cneuron%3B%2Cc0%3B%2Cs0%3B%3Bneuron%3B%2Cc0%3B%3BNeuron%3B%2Cc0%3B%3BNEURON%3B%2Cc0%3B.t4%3B%2Cneurone%3B%2Cc0%3B%2Cs0%3B%3Bneurone%3B%2Cc0%3B%3BNeurone%3B%2Cc0%3B%3BNEURONE%3B%2Cc0 |website=books.google.com |access-date=19 December 2020 |language=en}}</ref><ref name="oed"/>

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~~这个词以前在法语中被采用，拼写为neurone。这种拼法也曾被许多英语作家使用，~~[38]但现在在美国的用法中已经很少见，在英国的用法中也不常见。~~[39] [37]~~

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这个词以前在法语中被采用，拼写为'neurone'。<ref name="mehta">{{cite journal | vauthors = Mehta AR, Mehta PR, Anderson SP, MacKinnon BL, Compston A | title = Grey Matter Etymology and the neuron(e) | journal = Brain | volume = 143 | issue = 1 | pages = 374–379 | date = January 2020 | pmid = 31844876 | pmc = 6935745 | doi = 10.1093/brain/awz367 | url = }}</ref>这种拼法也曾被许多英语作家使用，[38]但现在在美国的用法中已经很少见，在英国的用法中也不常见。<ref name="ngram">{{cite web |title=Google Books Ngram Viewer |url=https://books.google.com/ngrams/graph?content=neuron%2Cneurone&year_start=1900&year_end=2008&case_insensitive=on&corpus=15&smoothing=3&direct_url=t4%3B%2Cneuron%3B%2Cc0%3B%2Cs0%3B%3Bneuron%3B%2Cc0%3B%3BNeuron%3B%2Cc0%3B%3BNEURON%3B%2Cc0%3B.t4%3B%2Cneurone%3B%2Cc0%3B%2Cs0%3B%3Bneurone%3B%2Cc0%3B%3BNeurone%3B%2Cc0%3B%3BNEURONE%3B%2Cc0 |website=books.google.com |access-date=19 December 2020 |language=en}}</ref><ref name="oed"/>

==History历史==

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The neuron's place as the primary functional unit of the nervous system was first recognized in the late 19th century through the work of the Spanish anatomist [[Santiago Ramón y Cajal]].<ref name="López-Muñoz">{{cite journal | vauthors = López-Muñoz F, Boya J, Alamo C | title = Neuron theory, the cornerstone of neuroscience, on the centenary of the Nobel Prize award to Santiago Ramón y Cajal | journal = Brain Research Bulletin | volume = 70 | issue = 4–6 | pages = 391–405 | date = October 2006 | pmid = 17027775 | doi = 10.1016/j.brainresbull.2006.07.010 | s2cid = 11273256 }}</ref>

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神经元作为神经系统主要功能单位的地位，在19世纪末通过西班牙解剖学家圣地亚哥-拉蒙-卡亚尔的作品首次得到承认。~~[40]~~

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神经元作为神经系统主要功能单位的地位，在19世纪末通过西班牙解剖学家圣地亚哥-拉蒙-卡亚尔的作品首次得到承认。<ref name="López-Muñoz">{{cite journal | vauthors = López-Muñoz F, Boya J, Alamo C | title = Neuron theory, the cornerstone of neuroscience, on the centenary of the Nobel Prize award to Santiago Ramón y Cajal | journal = Brain Research Bulletin | volume = 70 | issue = 4–6 | pages = 391–405 | date = October 2006 | pmid = 17027775 | doi = 10.1016/j.brainresbull.2006.07.010 | s2cid = 11273256 }}</ref>

To make the structure of individual neurons visible, [[Santiago Ramón y Cajal|Ramón y Cajal]] improved a [[Golgi's method|silver staining process]] that had been developed by [[Camillo Golgi]].<ref name="López-Muñoz" /> The improved process involves a technique called "double impregnation" and is still in use.

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为了使单个神经元的结构清晰可见，Ramón y Cajal改进了Camillo Golgi开发的银染工艺。~~[40]~~改进后的工艺涉及一种称为 "双浸渍 "的技术，现在仍在使用。

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为了使单个神经元的结构清晰可见，Ramón y Cajal改进了Camillo Golgi开发的银染工艺。<ref name="López-Muñoz" />改进后的工艺涉及一种称为 "双浸渍 "的技术，现在仍在使用。

In 1888 Ramón y Cajal published a paper about the bird cerebellum. In this paper, he stated that he could not find evidence for [[anastomosis]] between axons and dendrites and called each nervous element "an absolutely autonomous canton."<ref name="López-Muñoz" /><ref name="finger">{{Cite book|title=Origins of neuroscience : a history of explorations into brain function|last=Finger|first=Stanley|publisher=Oxford University Press|year=1994|url=https://www.google.com/books/edition/_/BdRqAAAAMAAJ?hl=en&gbpv=1&pg=PA47|isbn=9780195146943|oclc=27151391|page=47 |quote=Ramon y Cajal's first paper on the Golgi stain was on the bird cerebellum, and it appeared in the ''Revista''<nowiki> in 1888. He acknowledged that he found the nerve fibers to be very intricate, but stated that he could find no evidence for either axons or dendrites undergoing anastomosis and forming nets. He called each nervous element 'an absolutely autonomous canton.'</nowiki>}}</ref> This became known as the [[neuron doctrine]], one of the central tenets of modern [[neuroscience]].<ref name="López-Muñoz" />

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1888年，Ramón y Cajal发表了一篇关于鸟类小脑的论文。在这篇论文中，他说他找不到轴突和树突之间结合的证据，并称每个神经元素为 "一个绝对自主的州县"~~[40] [36]~~，这被称为神经元学说，是现代神经科学的核心原则之一。~~[40]~~

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1888年，Ramón y Cajal发表了一篇关于鸟类小脑的论文。在这篇论文中，他说他找不到轴突和树突之间结合的证据，并称每个神经元素为 "一个绝对自主的州县"<ref name="López-Muñoz" /><ref name="finger">{{Cite book|title=Origins of neuroscience : a history of explorations into brain function|last=Finger|first=Stanley|publisher=Oxford University Press|year=1994|url=https://www.google.com/books/edition/_/BdRqAAAAMAAJ?hl=en&gbpv=1&pg=PA47|isbn=9780195146943|oclc=27151391|page=47 |quote=Ramon y Cajal's first paper on the Golgi stain was on the bird cerebellum, and it appeared in the ''Revista''<nowiki> in 1888. He acknowledged that he found the nerve fibers to be very intricate, but stated that he could find no evidence for either axons or dendrites undergoing anastomosis and forming nets. He called each nervous element 'an absolutely autonomous canton.'</nowiki>}}</ref>，这被称为神经元学说，是现代神经科学的核心原则之一。<ref name="López-Muñoz" />

In 1891, the German anatomist [[Heinrich Wilhelm Gottfried von Waldeyer-Hartz|Heinrich Wilhelm Waldeyer]] wrote a highly influential review of the neuron doctrine in which he introduced the term ''neuron'' to describe the anatomical and physiological unit of the nervous system.<ref>{{Cite book|title=Origins of neuroscience : a history of explorations into brain function|last=Finger|first=Stanley|publisher=Oxford University Press|year=1994|url=https://www.google.com/books/edition/_/BdRqAAAAMAAJ?hl=en&gbpv=1&pg=PA47|isbn=9780195146943|oclc=27151391|page=47 |quote=... a man who would write a highly influential review of the evidence in favor of the neuron doctrine two years later. In his paper, Waldeyer (1891), ... , wrote that nerve cells terminate freely with end arborizations and that the 'neuron' is the anatomical and physiological unit of the nervous system. The word 'neuron' was born this way.}}</ref><ref>{{cite web|url=http://www.whonamedit.com/doctor.cfm/1846.html|title=Whonamedit - dictionary of medical eponyms|website=www.whonamedit.com|quote=Today, Wilhelm von Waldeyer-Hartz is remembered as the founder of the neurone theory, coining the term "neurone" to describe the cellular function unit of the nervous system and enunciating and clarifying that concept in 1891.}}</ref>

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1891年，德国解剖学家Heinrich Wilhelm Waldeyer写了一篇对神经元学说有很大影响的综述，他在其中提出了神经元这一术语来描述神经系统的解剖学和生理学单位。~~[41] [42]~~

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1891年，德国解剖学家Heinrich Wilhelm Waldeyer写了一篇对神经元学说有很大影响的综述，他在其中提出了神经元这一术语来描述神经系统的解剖学和生理学单位。<ref>{{Cite book|title=Origins of neuroscience : a history of explorations into brain function|last=Finger|first=Stanley|publisher=Oxford University Press|year=1994|url=https://www.google.com/books/edition/_/BdRqAAAAMAAJ?hl=en&gbpv=1&pg=PA47|isbn=9780195146943|oclc=27151391|page=47 |quote=... a man who would write a highly influential review of the evidence in favor of the neuron doctrine two years later. In his paper, Waldeyer (1891), ... , wrote that nerve cells terminate freely with end arborizations and that the 'neuron' is the anatomical and physiological unit of the nervous system. The word 'neuron' was born this way.}}</ref><ref>{{cite web|url=http://www.whonamedit.com/doctor.cfm/1846.html|title=Whonamedit - dictionary of medical eponyms|website=www.whonamedit.com|quote=Today, Wilhelm von Waldeyer-Hartz is remembered as the founder of the neurone theory, coining the term "neurone" to describe the cellular function unit of the nervous system and enunciating and clarifying that concept in 1891.}}</ref>

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The silver impregnation stains are a useful method for [[Neuroanatomy|neuroanatomical]] investigations because, for reasons unknown, it stains only a small percentage of cells in a tissue, exposing the complete micro structure of individual neurons without much overlap from other cells.<ref name="Grant">{{cite journal | vauthors = Grant G | title = How the 1906 Nobel Prize in Physiology or Medicine was shared between Golgi and Cajal | journal = Brain Research Reviews | volume = 55 | issue = 2 | pages = 490–8 | date = October 2007 | pmid = 17306375 | doi = 10.1016/j.brainresrev.2006.11.004 | s2cid = 24331507 }}</ref>

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银浸渍染色法是神经解剖学研究的有效方法，因为——由于未知的原因——它只会对组织中的一小部分细胞进行染色，暴露出单个神经元的完整微观结构，而不会与其他细胞有太多的重叠。~~[43]~~

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银浸渍染色法是神经解剖学研究的有效方法，因为——由于未知的原因——它只会对组织中的一小部分细胞进行染色，暴露出单个神经元的完整微观结构，而不会与其他细胞有太多的重叠。<ref name="Grant">{{cite journal | vauthors = Grant G | title = How the 1906 Nobel Prize in Physiology or Medicine was shared between Golgi and Cajal | journal = Brain Research Reviews | volume = 55 | issue = 2 | pages = 490–8 | date = October 2007 | pmid = 17306375 | doi = 10.1016/j.brainresrev.2006.11.004 | s2cid = 24331507 }}</ref>

===Neuron doctrine神经元学说===

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Later discoveries yielded refinements to the doctrine. For example, [[Neuroglia|glial cells]], which are non-neuronal, play an essential role in information processing.<ref>{{cite journal | vauthors = Witcher MR, Kirov SA, Harris KM | title = Plasticity of perisynaptic astroglia during synaptogenesis in the mature rat hippocampus | journal = Glia | volume = 55 | issue = 1 | pages = 13–23 | date = January 2007 | pmid = 17001633 | doi = 10.1002/glia.20415 | citeseerx = 10.1.1.598.7002 | s2cid = 10664003 }}</ref> Also, electrical synapses are more common than previously thought,<ref>{{cite journal | vauthors = Connors BW, Long MA | title = Electrical synapses in the mammalian brain | journal = Annual Review of Neuroscience | volume = 27 | issue = 1 | pages = 393–418 | year = 2004 | pmid = 15217338 | doi = 10.1146/annurev.neuro.26.041002.131128 | url = https://zenodo.org/record/894386 }}</ref> comprising direct, cytoplasmic connections between neurons. In fact, neurons can form even tighter couplings: the squid giant axon arises from the fusion of multiple axons.<ref>{{cite journal | vauthors = Guillery RW | title = Observations of synaptic structures: origins of the neuron doctrine and its current status | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 360 | issue = 1458 | pages = 1281–307 | date = June 2005 | pmid = 16147523 | pmc = 1569502 | doi = 10.1098/rstb.2003.1459 }}</ref>

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后来的发现使这一学说得到了完善。例如，非神经元的胶质细胞在信息处理中起着至关重要的作用。~~[44]~~ 另外，电突触比以前认为得更常见，~~[45]~~ 包括神经元之间的直接胞质连接。事实上，神经元可以形成更紧密的耦合：乌贼的巨型轴突来自于多个轴突的融合。~~[46]~~

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后来的发现使这一学说得到了完善。例如，非神经元的胶质细胞在信息处理中起着至关重要的作用。<ref>{{cite journal | vauthors = Witcher MR, Kirov SA, Harris KM | title = Plasticity of perisynaptic astroglia during synaptogenesis in the mature rat hippocampus | journal = Glia | volume = 55 | issue = 1 | pages = 13–23 | date = January 2007 | pmid = 17001633 | doi = 10.1002/glia.20415 | citeseerx = 10.1.1.598.7002 | s2cid = 10664003 }}</ref>另外，电突触比以前认为得更常见，<ref>{{cite journal | vauthors = Connors BW, Long MA | title = Electrical synapses in the mammalian brain | journal = Annual Review of Neuroscience | volume = 27 | issue = 1 | pages = 393–418 | year = 2004 | pmid = 15217338 | doi = 10.1146/annurev.neuro.26.041002.131128 | url = https://zenodo.org/record/894386 }}</ref>包括神经元之间的直接胞质连接。事实上，神经元可以形成更紧密的耦合：乌贼的巨型轴突来自于多个轴突的融合。<ref>{{cite journal | vauthors = Guillery RW | title = Observations of synaptic structures: origins of the neuron doctrine and its current status | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 360 | issue = 1458 | pages = 1281–307 | date = June 2005 | pmid = 16147523 | pmc = 1569502 | doi = 10.1098/rstb.2003.1459 }}</ref>

Ramón y Cajal also postulated the Law of Dynamic Polarization, which states that a neuron receives signals at its dendrites and cell body and transmits them, as action potentials, along the axon in one direction: away from the cell body.<ref name="sabb">{{cite journal | vauthors = Sabbatini RM | date = April–July 2003 | url = http://www.cerebromente.org.br/n17/history/neurons3_i.htm | title = Neurons and Synapses: The History of Its Discovery | journal = Brain & Mind Magazine | pages = 17 }}</ref> The Law of Dynamic Polarization has important exceptions; dendrites can serve as synaptic output sites of neurons<ref>{{cite journal | vauthors = Djurisic M, Antic S, Chen WR, Zecevic D | title = Voltage imaging from dendrites of mitral cells: EPSP attenuation and spike trigger zones | journal = The Journal of Neuroscience | volume = 24 | issue = 30 | pages = 6703–14 | date = July 2004 | pmid = 15282273 | pmc = 6729725 | doi = 10.1523/JNEUROSCI.0307-04.2004 | hdl = 1912/2958 }}

</ref> and axons can receive synaptic inputs.<ref>{{cite journal | vauthors = Cochilla AJ, Alford S | title = Glutamate receptor-mediated synaptic excitation in axons of the lamprey | journal = The Journal of Physiology | volume = 499 | issue = Pt 2 | pages = 443–57 | date = March 1997 | pmid = 9080373 | pmc = 1159318 | doi = 10.1113/jphysiol.1997.sp021940 }}</ref>

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拉蒙-卡哈尔还提出了动态极化定律，即神经元在其树突和细胞体上接收信号，并作为动作电位沿轴突向一个方向传输：离开细胞体。~~[47]~~ 动态极化定律有重要的例外；树突可以作为神经元的突触输出点~~[48]~~ ，轴突可以接受突触输入。~~[49]~~

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拉蒙-卡哈尔还提出了动态极化定律，即神经元在其树突和细胞体上接收信号，并作为动作电位沿轴突向一个方向传输：离开细胞体。<ref name="sabb">{{cite journal | vauthors = Sabbatini RM | date = April–July 2003 | url = http://www.cerebromente.org.br/n17/history/neurons3_i.htm | title = Neurons and Synapses: The History of Its Discovery | journal = Brain & Mind Magazine | pages = 17 }}</ref> 动态极化定律有重要的例外；树突可以作为神经元的突触输出点<ref>{{cite journal | vauthors = Djurisic M, Antic S, Chen WR, Zecevic D | title = Voltage imaging from dendrites of mitral cells: EPSP attenuation and spike trigger zones | journal = The Journal of Neuroscience | volume = 24 | issue = 30 | pages = 6703–14 | date = July 2004 | pmid = 15282273 | pmc = 6729725 | doi = 10.1523/JNEUROSCI.0307-04.2004 | hdl = 1912/2958 }}

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</ref>，轴突可以接受突触输入。<ref>{{cite journal | vauthors = Cochilla AJ, Alford S | title = Glutamate receptor-mediated synaptic excitation in axons of the lamprey | journal = The Journal of Physiology | volume = 499 | issue = Pt 2 | pages = 443–57 | date = March 1997 | pmid = 9080373 | pmc = 1159318 | doi = 10.1113/jphysiol.1997.sp021940 }}</ref>

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===Compartmental modelling of neurons 神经元的间室模型===

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Although neurons are often described of as "fundamental units" of the brain, they perform internal computations. Neurons integrate input within dendrites, and this complexity is lost in models that assume neurons to be a fundamental unit. Dendritic branches can be modeled as spatial compartments, whose activity is related due to passive membrane properties, but may also be different depending on input from synapses. [[Compartmental modelling of dendrites]] is especially helpful for understanding the behavior of neurons that are too small to record with electrodes, as is the case for ''Drosophila melanogaster''.<ref>{{cite journal | vauthors = Gouwens NW, Wilson RI | title = Signal propagation in Drosophila central neurons | journal = Journal of Neuroscience | volume = 29 | issue = 19 | pages = 6239–6249 | year = 2009 | pmid = 19439602 | pmc = 2709801 | doi = 10.1523/jneurosci.0764-09.2009 | doi-access = free }}</ref>

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尽管神经元经常被描述为大脑的 "基本单位"，但它们执行内部计算。神经元在树突内整合输入，这种复杂性在假定神经元是一个基本单位的模型中丢失。树突分支可以被建模为空间隔间，其活性与被动膜特性相关，但也可能因来自突触的输入的差异而有所不同。树突的间室模型对于理解那些太小而无法用电极记录的神经元的行为特别有帮助，黑腹果蝇就是这种情况。~~[50]~~

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尽管神经元经常被描述为大脑的 "基本单位"，但它们执行内部计算。神经元在树突内整合输入，这种复杂性在假定神经元是一个基本单位的模型中丢失。树突分支可以被建模为空间隔间，其活性与被动膜特性相关，但也可能因来自突触的输入的差异而有所不同。树突的间室模型对于理解那些太小而无法用电极记录的神经元的行为特别有帮助，黑腹果蝇就是这种情况。<ref>{{cite journal | vauthors = Gouwens NW, Wilson RI | title = Signal propagation in Drosophila central neurons | journal = Journal of Neuroscience | volume = 29 | issue = 19 | pages = 6239–6249 | year = 2009 | pmid = 19439602 | pmc = 2709801 | doi = 10.1523/jneurosci.0764-09.2009 | doi-access = free }}</ref>

==Neurons in the brain大脑中的神经元==

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The number of neurons in the brain varies dramatically from species to species.<ref name="nervenet">{{cite journal | vauthors = Williams RW, Herrup K | title = The control of neuron number | journal = Annual Review of Neuroscience | volume = 11 | issue = 1 | pages = 423–53 | year = 1988 | pmid = 3284447 | doi = 10.1146/annurev.ne.11.030188.002231 }}</ref> In a human, there are an estimated 10–20 billion neurons in the [[cerebral cortex]] and 55–70 billion neurons in the [[cerebellum]].<ref name="pmid27187682">{{cite journal | vauthors = von Bartheld CS, Bahney J, Herculano-Houzel S | title = The search for true numbers of neurons and glial cells in the human brain: A review of 150 years of cell counting | journal = The Journal of Comparative Neurology | volume = 524 | issue = 18 | pages = 3865–3895 | date = December 2016 | pmid = 27187682 | pmc = 5063692 | doi = 10.1002/cne.24040 }}</ref> By contrast, the [[nematode]] worm ''[[Caenorhabditis elegans]]'' has just 302 neurons, making it an ideal [[model organism]] as scientists have been able to map all of its neurons. The fruit fly ''[[Drosophila melanogaster]]'', a common subject in biological experiments, has around 100,000 neurons and exhibits many complex behaviors. Many properties of neurons, from the type of neurotransmitters used to ion channel composition, are maintained across species, allowing scientists to study processes occurring in more complex organisms in much simpler experimental systems.

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大脑中的神经元数量因物种不同而有很大差异。~~[51]~~ 在人类中，大脑皮层中估计有100-~~200亿个神经元，小脑中有550~~-700亿个神经元。~~[52]~~ 相比之下，秀丽隐杆线虫只有302个神经元，使其成为理想的模型生物，因为科学家已经能够绘制其所有的神经元。黑腹果蝇是生物实验中常见的对象，它有大约10万个神经元，表现出许多复杂的行为。神经元的许多特性，从使用的神经递质类型到离子通道组成，在不同的物种中都保持不变，使科学家能够在更简单的实验系统中研究发生在更复杂生物体中的过程。

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大脑中的神经元数量因物种不同而有很大差异。<ref name="nervenet">{{cite journal | vauthors = Williams RW, Herrup K | title = The control of neuron number | journal = Annual Review of Neuroscience | volume = 11 | issue = 1 | pages = 423–53 | year = 1988 | pmid = 3284447 | doi = 10.1146/annurev.ne.11.030188.002231 }}</ref>在人类中，大脑皮层中估计有100-200亿个神经元，小脑中有550-700亿个神经元。<ref name="pmid27187682">{{cite journal | vauthors = von Bartheld CS, Bahney J, Herculano-Houzel S | title = The search for true numbers of neurons and glial cells in the human brain: A review of 150 years of cell counting | journal = The Journal of Comparative Neurology | volume = 524 | issue = 18 | pages = 3865–3895 | date = December 2016 | pmid = 27187682 | pmc = 5063692 | doi = 10.1002/cne.24040 }}</ref>相比之下，秀丽隐杆线虫只有302个神经元，使其成为理想的模型生物，因为科学家已经能够绘制其所有的神经元。黑腹果蝇是生物实验中常见的对象，它有大约10万个神经元，表现出许多复杂的行为。神经元的许多特性，从使用的神经递质类型到离子通道组成，在不同的物种中都保持不变，使科学家能够在更简单的实验系统中研究发生在更复杂生物体中的过程。

==Neurological disorders神经系统疾病==

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'''[[Charcot–Marie–Tooth disease]]''' (CMT) is a heterogeneous inherited disorder of nerves ([[neuropathy]]) that is characterized by loss of muscle tissue and touch sensation, predominantly in the feet and legs extending to the hands and arms in advanced stages. Presently incurable, this disease is one of the most common inherited neurological disorders, with 36 in 100,000 affected.<ref name=Krajewski>{{cite journal | vauthors = Krajewski KM, Lewis RA, Fuerst DR, Turansky C, Hinderer SR, Garbern J, Kamholz J, Shy ME | title = Neurological dysfunction and axonal degeneration in Charcot-Marie-Tooth disease type 1A | journal = Brain | volume = 123 | issue = 7 | pages = 1516–27 | date = July 2000 | pmid = 10869062 | doi = 10.1093/brain/123.7.1516 | doi-access = free }}</ref>

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腓骨肌萎缩症（CMT）是一种异质性的遗传性神经疾病（神经病变），其特点是肌肉组织和触觉的丧失，主要是在脚和腿上，在晚期会延伸到手和胳膊。该病目前无法治愈，是最常见的遗传性神经系统疾病之一，每10万人中会有36人罹患此病。~~[53]~~

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腓骨肌萎缩症（CMT）是一种异质性的遗传性神经疾病（神经病变），其特点是肌肉组织和触觉的丧失，主要是在脚和腿上，在晚期会延伸到手和胳膊。该病目前无法治愈，是最常见的遗传性神经系统疾病之一，每10万人中会有36人罹患此病。<ref name=Krajewski>{{cite journal | vauthors = Krajewski KM, Lewis RA, Fuerst DR, Turansky C, Hinderer SR, Garbern J, Kamholz J, Shy ME | title = Neurological dysfunction and axonal degeneration in Charcot-Marie-Tooth disease type 1A | journal = Brain | volume = 123 | issue = 7 | pages = 1516–27 | date = July 2000 | pmid = 10869062 | doi = 10.1093/brain/123.7.1516 | doi-access = free }}</ref>

'''[[Alzheimer's disease]]''' (AD), also known simply as ''Alzheimer's'', is a [[neurodegenerative disease]] characterized by progressive [[cognitive]] deterioration, together with declining activities of daily living and [[neuropsychiatric]] symptoms or behavioral changes.<ref name="nihstages">{{cite web|title=About Alzheimer's Disease: Symptoms|url=http://www.nia.nih.gov/alzheimers/topics/symptoms|publisher=National Institute on Aging|access-date=28 December 2011|url-status=live|archive-url=https://web.archive.org/web/20120115201854/http://www.nia.nih.gov/alzheimers/topics/symptoms|archive-date=15 January 2012|df=dmy-all}}</ref> The most striking early symptom is loss of short-term memory ([[amnesia]]), which usually manifests as minor forgetfulness that becomes steadily more pronounced with illness progression, with relative preservation of older memories. As the disorder progresses, cognitive (intellectual) impairment extends to the domains of language ([[aphasia]]), skilled movements ([[apraxia]]), and recognition ([[agnosia]]), and functions such as decision-making and planning become impaired.<ref name="BMJ2009">{{cite journal | vauthors = Burns A, Iliffe S | title = Alzheimer's disease | journal = BMJ | volume = 338 | pages = b158 | date = February 2009 | pmid = 19196745 | doi = 10.1136/bmj.b158 | s2cid = 8570146 | url = https://semanticscholar.org/paper/0fccf0616b35e3bb427c3783a44777e4dc228713 }}</ref><ref name=NEJM2010>{{cite journal | vauthors = Querfurth HW, LaFerla FM | title = Alzheimer's disease | journal = The New England Journal of Medicine | volume = 362 | issue = 4 | pages = 329–44 | date = January 2010 | pmid = 20107219 | doi = 10.1056/NEJMra0909142 | s2cid = 205115756 | url = https://semanticscholar.org/paper/7bc445c5ddf7869b9f71a5390ff9e9e992533ee3 }}</ref>

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阿尔茨海默病（AD），也被简单地称为阿尔茨海默病，是一种神经退行性疾病，其特点是认知能力逐渐退化，伴随着日常生活活动能力下降和神经精神症状或行为变化。[54] 最突出的早期症状是短期记忆的丧失（失忆），通常表现为轻微的遗忘，随着病情的发展，遗忘的程度会逐渐加重，但老的记忆却记忆得相对清楚。随着病情的发展，认知（智力）损害扩展到语言（失语）、熟练动作（失用）和识别（失认）等领域，决策和计划等功能也会受到损害[55][56] 。

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阿尔茨海默病（AD），也被简单地称为阿尔茨海默病，是一种神经退行性疾病，其特点是认知能力逐渐退化，伴随着日常生活活动能力下降和神经精神症状或行为变化。<ref name="nihstages">{{cite web|title=About Alzheimer's Disease: Symptoms|url=http://www.nia.nih.gov/alzheimers/topics/symptoms|publisher=National Institute on Aging|access-date=28 December 2011|url-status=live|archive-url=https://web.archive.org/web/20120115201854/http://www.nia.nih.gov/alzheimers/topics/symptoms|archive-date=15 January 2012|df=dmy-all}}</ref>最突出的早期症状是短期记忆的丧失（失忆），通常表现为轻微的遗忘，随着病情的发展，遗忘的程度会逐渐加重，但老的记忆却记忆得相对清楚。随着病情的发展，认知（智力）损害扩展到语言（失语）、熟练动作（失用）和识别（失认）等领域，决策和计划等功能也会受到损害。<ref name="BMJ2009">{{cite journal | vauthors = Burns A, Iliffe S | title = Alzheimer's disease | journal = BMJ | volume = 338 | pages = b158 | date = February 2009 | pmid = 19196745 | doi = 10.1136/bmj.b158 | s2cid = 8570146 | url = https://semanticscholar.org/paper/0fccf0616b35e3bb427c3783a44777e4dc228713 }}</ref><ref name=NEJM2010>{{cite journal | vauthors = Querfurth HW, LaFerla FM | title = Alzheimer's disease | journal = The New England Journal of Medicine | volume = 362 | issue = 4 | pages = 329–44 | date = January 2010 | pmid = 20107219 | doi = 10.1056/NEJMra0909142 | s2cid = 205115756 | url = https://semanticscholar.org/paper/7bc445c5ddf7869b9f71a5390ff9e9e992533ee3 }}</ref>

'''[[Parkinson's disease]]''' (PD), also known as ''Parkinson disease'', is a degenerative disorder of the central nervous system that often impairs motor skills and speech.<ref name=NIH2016>{{cite web|title=Parkinson's Disease Information Page|url=https://www.ninds.nih.gov/Disorders/All-Disorders/Parkinsons-Disease-Information-Page|website=NINDS|access-date=18 July 2016|date=30 June 2016|url-status=live|archive-url=https://web.archive.org/web/20170104201403/http://www.ninds.nih.gov/Disorders/All-Disorders/Parkinsons-Disease-Information-Page|archive-date=4 January 2017|df=dmy-all}}</ref> Parkinson's disease belongs to a group of conditions called [[movement disorders]].<ref>{{cite web | title = Movement Disorders| url = http://www.neuromodulation.com/movement-disorders | work = The International Neuromodulation Society }}</ref> It is characterized by muscle rigidity, [[tremor]], a slowing of physical movement ([[bradykinesia]]), and in extreme cases, a loss of physical movement ([[akinesia]]). The primary symptoms are the results of decreased stimulation of the [[motor cortex]] by the [[basal ganglia]], normally caused by the insufficient formation and action of dopamine, which is produced in the dopaminergic neurons of the brain. Secondary symptoms may include high level [[cognitive dysfunction]] and subtle language problems. PD is both chronic and progressive.

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帕金森病（PD），又称帕金森病，是一种中枢神经系统的退行性疾病，通常会损害运动技能和语言能力。~~[57]~~ 帕金森病属于一组被称为运动障碍的疾病。~~[58]~~ 它的特点是肌肉僵硬、震颤、身体运动变慢（运动迟缓），在极端情况下，身体运动丧失（运动不能）。主要症状是基底神经节对运动皮层刺激减少的结果，通常是由于大脑多巴胺能神经元中产生的多巴胺形成和作用不足造成的。次要症状可能包括高水平的认知功能障碍和微妙的语言问题。帕金森病既是慢性的，也是渐进的。

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帕金森病（PD），又称帕金森病，是一种中枢神经系统的退行性疾病，通常会损害运动技能和语言能力。<ref name=NIH2016>{{cite web|title=Parkinson's Disease Information Page|url=https://www.ninds.nih.gov/Disorders/All-Disorders/Parkinsons-Disease-Information-Page|website=NINDS|access-date=18 July 2016|date=30 June 2016|url-status=live|archive-url=https://web.archive.org/web/20170104201403/http://www.ninds.nih.gov/Disorders/All-Disorders/Parkinsons-Disease-Information-Page|archive-date=4 January 2017|df=dmy-all}}</ref> 帕金森病属于一组被称为运动障碍的疾病。<ref>{{cite web | title = Movement Disorders| url = http://www.neuromodulation.com/movement-disorders | work = The International Neuromodulation Society }}</ref>它的特点是肌肉僵硬、震颤、身体运动变慢（运动迟缓），在极端情况下，身体运动丧失（运动不能）。主要症状是基底神经节对运动皮层刺激减少的结果，通常是由于大脑多巴胺能神经元中产生的多巴胺形成和作用不足造成的。次要症状可能包括高水平的认知功能障碍和微妙的语言问题。帕金森病既是慢性的，也是渐进的。

'''[[Myasthenia gravis]]''' is a neuromuscular disease leading to fluctuating [[muscle weakness]] and fatigability during simple activities. Weakness is typically caused by circulating [[antibodies]] that block [[acetylcholine receptors]] at the post-synaptic neuromuscular junction, inhibiting the stimulative effect of the neurotransmitter acetylcholine. Myasthenia is treated with [[immunosuppressants]], [[cholinesterase]] inhibitors and, in selected cases, [[thymectomy]].

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[[Adult neurogenesis]] can occur and studies of the age of human neurons suggest that this process occurs only for a minority of cells, and that the vast majority of neurons in the [[neocortex]] forms before birth and persists without replacement. The extent to which adult neurogenesis exists in humans, and its contribution to cognition are controversial, with conflicting reports published in 2018.<ref>{{cite journal | vauthors = Kempermann G, Gage FH, Aigner L, Song H, Curtis MA, Thuret S, Kuhn HG, Jessberger S, Frankland PW, Cameron HA, Gould E, Hen R, Abrous DN, Toni N, Schinder AF, Zhao X, Lucassen PJ, Frisén J | title = Human Adult Neurogenesis: Evidence and Remaining Questions | journal = Cell Stem Cell | volume = 23 | issue = 1 | pages = 25–30 | date = July 2018 | pmid = 29681514 | pmc = 6035081 | doi = 10.1016/j.stem.2018.04.004 }}</ref>

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成年神经发生能够发生，对人类神经元年龄的研究表明，这一过程只发生在少数细胞中，新皮层中的绝大多数神经元在出生前就已形成，并持续存在而不被替换。人类中成年神经发生存在的程度，以及它对认知的贡献是有争议的，2018年发表的报告相互矛盾。~~[59]~~

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成年神经发生能够发生，对人类神经元年龄的研究表明，这一过程只发生在少数细胞中，新皮层中的绝大多数神经元在出生前就已形成，并持续存在而不被替换。人类中成年神经发生存在的程度，以及它对认知的贡献是有争议的，2018年发表的报告相互矛盾。<ref>{{cite journal | vauthors = Kempermann G, Gage FH, Aigner L, Song H, Curtis MA, Thuret S, Kuhn HG, Jessberger S, Frankland PW, Cameron HA, Gould E, Hen R, Abrous DN, Toni N, Schinder AF, Zhao X, Lucassen PJ, Frisén J | title = Human Adult Neurogenesis: Evidence and Remaining Questions | journal = Cell Stem Cell | volume = 23 | issue = 1 | pages = 25–30 | date = July 2018 | pmid = 29681514 | pmc = 6035081 | doi = 10.1016/j.stem.2018.04.004 }}</ref>

The body contains a variety of stem cell types that have the capacity to differentiate into neurons. Researchers found a way to transform human skin cells into nerve cells using [[transdifferentiation]], in which "cells are forced to adopt new identities".<ref name=twsX33>{{Cite journal |doi=10.1038/news.2011.328 | last = Callaway | first = Ewen |title= How to make a human neuron | journal = Nature |quote= By transforming cells from human skin into working nerve cells, researchers may have come up with a model for nervous-system diseases and perhaps even regenerative therapies based on cell transplants. The achievement, reported online today in ''Nature'', is the latest in a fast-moving field called transdifferentiation, in which cells are forced to adopt new identities. In the past year, researchers have converted connective tissue cells found in skin into heart cells, blood cells, and liver cells.

|date= 26 May 2011 }}</ref>

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人体含有各种干细胞类型，它们有能力分化为神经元。研究人员发现了一种利用横向分化将人类皮肤细胞转化为神经细胞的方法，其中 "细胞被迫采用新的身份"。~~[60]~~

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人体含有各种干细胞类型，它们有能力分化为神经元。研究人员发现了一种利用横向分化将人类皮肤细胞转化为神经细胞的方法，其中 "细胞被迫采用新的身份"。<ref name=twsX33>{{Cite journal |doi=10.1038/news.2011.328 | last = Callaway | first = Ewen |title= How to make a human neuron | journal = Nature |quote= By transforming cells from human skin into working nerve cells, researchers may have come up with a model for nervous-system diseases and perhaps even regenerative therapies based on cell transplants. The achievement, reported online today in ''Nature'', is the latest in a fast-moving field called transdifferentiation, in which cells are forced to adopt new identities. In the past year, researchers have converted connective tissue cells found in skin into heart cells, blood cells, and liver cells.

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|date= 26 May 2011 }}</ref>

During [[neurogenesis]] in the mammalian brain, progenitor and stem cells progress from proliferative divisions to differentiative divisions. This progression leads to the neurons and glia that populate cortical layers. [[Epigenetics|Epigenetic]] modifications play a key role in regulating [[gene expression]] in differentiating [[neural stem cells]], and are critical for cell fate determination in the developing and adult mammalian brain. Epigenetic modifications include [[DNA methylation|DNA cytosine methylation]] to form [[5-methylcytosine]] and [[DNA demethylation|5-methylcytosine demethylation]].<ref name=Wang2016>{{cite journal | vauthors = Wang Z, Tang B, He Y, Jin P | title = DNA methylation dynamics in neurogenesis | journal = Epigenomics | volume = 8 | issue = 3 | pages = 401–14 | date = March 2016 | pmid = 26950681 | pmc = 4864063 | doi = 10.2217/epi.15.119 }}</ref> These modifications are critical for cell fate determination in the developing and adult mammalian brain. [[DNA methylation|DNA cytosine methylation]] is catalyzed by [[DNA methyltransferase|DNA methyltransferases (DNMTs)]]. Methylcytosine demethylation is catalyzed in several stages by [[TET enzymes]] that carry out oxidative reactions (e.g. [[5-methylcytosine]] to [[5-hydroxymethylcytosine]]) and enzymes of the DNA [[base excision repair]] (BER) pathway.<ref name=Wang2016/>

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在哺乳动物大脑的神经发生过程中，祖细胞和干细胞从增殖性分裂发展到分化性分裂。这一进展导致了皮层中的神经元和胶质细胞的出现。表观遗传学修饰在调节分化中的神经干细胞的基因表达方面起着关键作用，对发育中和成年哺乳动物大脑中的细胞命运决定至关重要。表观遗传修饰包括DNA胞嘧啶甲基化形成5-甲基胞嘧啶和5-甲基胞嘧啶去甲基化。~~[61]~~ 这些修饰对于发育中和成年哺乳动物大脑的细胞命运决定至关重要。DNA胞嘧啶甲基化是由DNA甲基转移酶（DNMTs）催化的。甲基胞嘧啶去甲基化是由进行氧化反应（如5-甲基胞嘧啶到5-~~羟甲基胞嘧啶）的TET酶和DNA碱基切除修复（BER）途径的酶分几个阶段催化的[61] 。~~

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在哺乳动物大脑的神经发生过程中，祖细胞和干细胞从增殖性分裂发展到分化性分裂。这一进展导致了皮层中的神经元和胶质细胞的出现。表观遗传学修饰在调节分化中的神经干细胞的基因表达方面起着关键作用，对发育中和成年哺乳动物大脑中的细胞命运决定至关重要。表观遗传修饰包括DNA胞嘧啶甲基化形成5-甲基胞嘧啶和5-甲基胞嘧啶去甲基化。<ref name=Wang2016>{{cite journal | vauthors = Wang Z, Tang B, He Y, Jin P | title = DNA methylation dynamics in neurogenesis | journal = Epigenomics | volume = 8 | issue = 3 | pages = 401–14 | date = March 2016 | pmid = 26950681 | pmc = 4864063 | doi = 10.2217/epi.15.119 }}</ref>这些修饰对于发育中和成年哺乳动物大脑的细胞命运决定至关重要。DNA胞嘧啶甲基化是由DNA甲基转移酶（DNMTs）催化的。甲基胞嘧啶去甲基化是由进行氧化反应（如5-甲基胞嘧啶到5-羟甲基胞嘧啶）的TET酶和DNA碱基切除修复（BER）途径的酶分几个阶段催化的。<ref name=Wang2016/>

At different stages of mammalian nervous system development two DNA repair processes are employed in the repair of DNA double-strand breaks. These pathways are [[homologous recombination]]al repair used in proliferating neural precursor cells, and [[non-homologous end joining]] used mainly at later developmental stages<ref>{{cite journal | vauthors = Orii KE, Lee Y, Kondo N, McKinnon PJ | title = Selective utilization of nonhomologous end-joining and homologous recombination DNA repair pathways during nervous system development | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 103 | issue = 26 | pages = 10017–22 | date = June 2006 | pmid = 16777961 | pmc = 1502498 | doi = 10.1073/pnas.0602436103 | bibcode = 2006PNAS..10310017O | doi-access = free }}</ref>

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在哺乳动物神经系统发育的不同阶段，有两种DNA修复过程被用于修复DNA双链断裂。这些途径是用于增殖期神经前体细胞的同源重组修复，以及主要用于后期发育阶段的非同源末端连接[62] 。

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在哺乳动物神经系统发育的不同阶段，有两种DNA修复过程被用于修复DNA双链断裂。这些途径是用于增殖期神经前体细胞的同源重组修复，以及主要用于后期发育阶段的非同源末端连接。<ref>{{cite journal | vauthors = Orii KE, Lee Y, Kondo N, McKinnon PJ | title = Selective utilization of nonhomologous end-joining and homologous recombination DNA repair pathways during nervous system development | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 103 | issue = 26 | pages = 10017–22 | date = June 2006 | pmid = 16777961 | pmc = 1502498 | doi = 10.1073/pnas.0602436103 | bibcode = 2006PNAS..10310017O | doi-access = free }}</ref>

==Nerve regeneration神经再生==

第495行：第503行：

Peripheral axons can regrow if they are severed,<ref name="Yiu_2006">{{cite journal | vauthors = Yiu G, He Z | title = Glial inhibition of CNS axon regeneration | journal = Nature Reviews. Neuroscience | volume = 7 | issue = 8 | pages = 617–27 | date = August 2006 | pmid = 16858390 | pmc = 2693386 | doi = 10.1038/nrn1956 }}</ref> but one neuron cannot be functionally replaced by one of another type ([[Llinás' law]]).<ref name="llinas2014"/>

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外围轴突如果被切断，可以重新生长，~~[63]但一个神经元在功能上不能被另一种类型的神经元取代（Llinás法则）[15]。~~

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外围轴突如果被切断，可以重新生长，<ref name="Yiu_2006">{{cite journal | vauthors = Yiu G, He Z | title = Glial inhibition of CNS axon regeneration | journal = Nature Reviews. Neuroscience | volume = 7 | issue = 8 | pages = 617–27 | date = August 2006 | pmid = 16858390 | pmc = 2693386 | doi = 10.1038/nrn1956 }}</ref>但一个神经元在功能上不能被另一种类型的神经元取代（Llinás法则）。<ref name="llinas2014"/>

== See also ==

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